(Reuters Health) - When a bystander gives CPR or applies an automatic defibrillator to someone who has collapsed from cardiac arrest, the benefits persist for at least a year.

A Danish study has concluded that the two techniques lower the long-term risk of death from any cause, brain damage or nursing home admission by one third in people who are still alive 30 days after their cardiac arrest.

Most previous studies have looked at whether people who get CPR or defibrillation manage to survive or escape serious injury by the 30-day mark.

"This science provides the linkage to show that resuscitation is not just important in the immediate cardiac arrest phase, but it's an important factor into whether they go back to their lives intact," said Dr. Michael Kurz, associate professor of emergency medicine at the University of Alabama-Birmingham Medicine, who was not involved in the study.

"We were surprised to see that, once you select 30-day survivors, so many were still alive at one year and the majority of these survivors seemed to have a fairly good outcome," study coauthor Dr. Kristian Kragholm told Reuters Health in a telephone interview. "If bystanders intervened by starting chest compression, survivors were less likely to experience brain damage or be admitted to a nursing home. And with an AED (automated external defibrillator), the benefit was even greater."

For the public, it's further evidence "of what you can do when you witness a cardiac arrest," and why policy makers should be working harder to both require resuscitation training for the general public and make more defibrillators available in public places, said Kragholm, of Aalborg University Hospital in Denmark.

The study, published in the New England Journal of Medicine, used national registries to identify 34,459 people who had received some type of bystander resuscitation when they had cardiac arrest outside of a hospital. Only 8.3 percent survived for a month.

But with bystander CPR, the odds of subsequent death from any cause at one year among the 30-day survivors were 30 percent lower, the likelihood of brain damage or nursing home admission was 38 percent lower and the rate of all three outcomes combined was 33 percent lower.

With bystander defibrillation, the death rate was 78 percent lower, the composite of brain damage or nursing home admission was 55 percent lower and the odds for the combination of all three were also 55 percent lower. But the number of cases where a defibrillator was used was relatively small, even though the automated devices are becoming more common.

Over all, the risk of brain damage or a nursing home admission was just 3.7 percent if the cardiac arrest was witnessed by emergency medical service personnel. If bystanders used defibrillation, the rate was 8.4 percent. If bystanders used CPR alone it was 12.1 percent. The danger was highest - 18.6 percent - when no bystander resuscitation was done.

"This underpins the importance of the public to identify and respond to that emergency," Kurz said. "Denmark has a very impressive bystander CPR rate. That's one of the reasons the numbers in this article are so good."

During the study, which ran from 2001 through 2012, the rate of bystander CPR went from 67 percent of the cases to 81 percent, and the rate of bystander defibrillation jumped from 2 percent to nearly 17 percent.

"Such increases are probably related to the multiple nationwide initiatives that have been taken in Denmark, including widespread mandatory and voluntary CPR training; widespread dissemination of automated external defibrillators; the introduction of health care professionals at emergency dispatch centers, facilitating dispatcher-assisted CPR; and the formation and linkage of an automated external defibrillator registry to the dispatch centers, enabling health care professionals to guide bystanders to the nearest automated external defibrillators," Kurz said.

Bystanders themselves can also locate the nearest automated external defibrillator with the use of a smartphone application.

CPR education became mandatory in schools in 2005 and for people acquiring a driver's license in 2006, according to Kragholm.

Kurz said that in the United States, defibrillators should be required in local building codes the way communities require fire alarms, smoke detectors and fire extinguishers.